Geomorphic evidence for post‐10 Ma uplift of the western flank of the central Andes 18°30′–22°S

Abstract

The western Andean mountain front forms the western edge of the central Andean Plateau. Between 18.5° and 22°S latitude, the mountain front has ∼3000 m of relief over ∼50 km horizontal distance that has developed in the absence of major local Neogene deformation. Models of the evolution of the plateau, as well as paleoaltimetry estimates, all call for continued large‐magnitude uplift of the plateau surface into the late Miocene (i.e., younger than 10 Ma). Longitudinal river profiles from 20 catchments that drain the western Andean mountain front contain several streams with knickpoint‐bounded segments that we use to reconstruct the history of post‐10 Ma surface uplift of the western flank of the central Andean Plateau. The generation of knickpoints is attributed to tectonic processes and is not a consequence of base level change related to Pacific Ocean capture, eustatic change, or climate change as causes for creating the knickpoint‐bounded stream segments observed. Minor valley‐filling alluvial gravels intercalated with the 5.4 Ma Carcote ignimbrite suggest uplift related river incision was well under way by 5.4 Ma. The maximum age of river incision is provided by the regionally extensive, approximately 10 Ma El Diablo–Altos de Pica paleosurface. The river profiles reveal that relative surface uplift of at least1 km occurred after 10 Ma.